[PATCH v3 24/45] infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline

[Srivatsa S. Bhat]

Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Hoang-Nam Nguyen <hnguyen at de.ibm.com>
Cc: Christoph Raisch <raisch at de.ibm.com>
Cc: Roland Dreier <roland at kernel.org>
Cc: Sean Hefty <sean.hefty at intel.com>
Cc: Hal Rosenstock <hal.rosenstock at gmail.com>
Cc: linux-rdma at vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
---

 drivers/infiniband/hw/ehca/ehca_irq.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c
index 8615d7c..ace901e 100644
--- a/drivers/infiniband/hw/ehca/ehca_irq.c
+++ b/drivers/infiniband/hw/ehca/ehca_irq.c
@@ -43,6 +43,7 @@
 
 #include <linux/slab.h>
 #include <linux/smpboot.h>
+#include <linux/cpu.h>
 
 #include "ehca_classes.h"
 #include "ehca_irq.h"
@@ -703,6 +704,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
 	int cq_jobs;
 	unsigned long flags;
 
+	get_online_cpus_atomic();
 	cpu_id = find_next_online_cpu(pool);
 	BUG_ON(!cpu_online(cpu_id));
 
@@ -720,6 +722,7 @@ static void queue_comp_task(struct ehca_cq *__cq)
 		BUG_ON(!cct || !thread);
 	}
 	__queue_comp_task(__cq, cct, thread);
+	put_online_cpus_atomic();
 }
 
 static void run_comp_task(struct ehca_cpu_comp_task *cct)
@@ -759,6 +762,7 @@ static void comp_task_park(unsigned int cpu)
 	list_splice_init(&cct->cq_list, &list);
 	spin_unlock_irq(&cct->task_lock);
 
+	get_online_cpus_atomic();
 	cpu = find_next_online_cpu(pool);
 	target = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
 	thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu);
@@ -768,6 +772,7 @@ static void comp_task_park(unsigned int cpu)
 		__queue_comp_task(cq, target, thread);
 	}
 	spin_unlock_irq(&target->task_lock);
+	put_online_cpus_atomic();
 }
 
 static void comp_task_stop(unsigned int cpu, bool online)